Even though the sale of the expansive archdiocesan campus to Boston College had long been expected by residents of the serene tree-lined blocks around the Brighton property, few neighbors were prepared yesterday for the news that the college is buying more than 40 acres in the neighborhood, 15 acres more than originally anticipated. Perhaps even more unnerving for some was the way the deal was done: sealed between the buyer and seller, with no consultation with the neighbors.

"The diocese wouldn't talk to us,'' lamented Arturo Vasquez, president of the Brighton-Allston Improvement Association and cochairman of the Allston-Brighton-Boston College Community Task Force. "Nobody knew this was coming." With Harvard University's purchase last year of 91 acres in Allston and Boston University's existing holdings in the neighborhood, Vasquez and others predicted that yesterday's sale will force many longtime residents who may have been holding out to start hanging out for sale signs, to avoid living next door to students.

"There is a ripple effect beyond universities coming in and buying up property," Vasquez said. He said he worried that real estate speculators will soon begin snapping up more properties in the area so they can "chop them up and rent them to students," which will turn more of the neighborhood into veritable dormitories, regardless of what Boston College does with its land.

"Maybe we'll be like Rumpelstiltskin," Vasquez said. "When we wake up in 10 years, we'll be renting from these institutions, because they'll own everything."

For its part, the Boston Redevelopment Authority maintained yesterday that it will be a vigilant guardian of the neighborhood, helping to oversee development, especially the college's longterm plan for the land there.

"This is going to be a long process," said Susan Elsbree, spokeswoman for the authority. "We know that institutions have a significant impact on the surrounding communities and the city as a whole, and we will work with the neighborhood and the college to come up with a plan and mitigate impacts."

BC officials maintained yesterday that the land will not get the high-density use that might upset neighbors and that it will instead be used for administrative offices, parking, and playing fields. The college also pledged to work with city officials before developing the land.

The serenity of the residential neighborhood around the chancery was apparent yesterday, as an elderly couple took an afternoon stroll. A couple of seminary students gripped strings of rosary beads in their hands as they walked down Lake Street, heads bowed. A dog tied to a tree wagged its tail as they passed.

John Brennan relaxed on his front balcony overlooking Lake Street and the archdiocesan tribunal building. Brennan said he was disappointed by the church's land sale agreement, but saddened and shocked by the bigger picture, that the sexual abuse by Catholic priests would affect him in such a personal way. The impending sale of the land, which will help pay to settle abuse victims' claims, could eventually transform his neighborhood from a peaceful residential sliver anchored by the church to a college-centered area with more traffic, more pollution, higher real estate prices, and more noisy students.

"You can't make up a story like that," Brennan said, shaking his head. "It would be different if they were selling it for some really good reason, like improving the church. But paying off abuse victims -- " His voice trailed off, then he added, "I just think it's sad."

Brennan, who has lived in the area for more than 15 years, was one of many residents who harbored hope until yesterday that city officials would step in and help preserve the archdiocesan land for open space.

Paul Berkeley, vice chairman of the Allston Brighton-Boston College Community Task Force, said the sale threatens one of the neighborhood's last open spaces.

"It's nice now to have a lot of green space near our homes," he said during a task force meeting last night with college officials. "If they make this into a student residential village, that would be disastrous. We need to be part of all their planning."

Many city officials interviewed said they were not notified of the sale agreement until yesterday.

City Council President Michael Flaherty said he had extracted a promise from the archdiocese months ago to work with him and other city officials before selling the land. But yesterday he decried "another broken promise from church leaders."

"They promised to work with us and they haven't," Flaherty said, minutes after receiving word of the sale at noon yesterday. "A last-minute fax announcing the sale is too little, too late. Are they going to announce the closing of parishes and schools in the same way, when everything is a done deal?"

For some, yesterday's announcement was another sign of the vast and painful challenges confronting the Roman Catholic Church in Boston.

In what church leaders say is an unrelated initiative, a significant but unspecified number of Catholic parishes and schools will be closed this year. Community leaders say the churches have served as anchors in urban neighborhoods, and they worry about the stability of those areas if they are shuttered.

With yesterday's agreement to sell the cardinal's mansion, along with St. Clement's Hall, where the archdiocese once trained high school seminarians; and St. William's Hall, where lay ministers were trained, the church appears to be having a "going out of business sale," remarked Secretary of State William F. Galvin, who has lived across the street from the archdiocese property in Brighton for 20 years. "As an institution, is this the end?" Galvin queried. "It's more than just a dramatic move, when you start selling off the educational facilities."

The archdiocese's land in Brighton is only a few blocks from the Newton border, and some elected officials there expressed cautious optimism yesterday about the sale. The city of Newton has clashed with Boston College in a protracted legal battle over several proposed college buildings. But Ward 7 Alderman Lisle Baker, who has dealt with Boston College's expansion plans into his ward for years, said that generally, relations with the college have been good.

"The college, in my experience, has been generally responsive, with some exceptions where there have been differences of opinion," Baker said. "But I think that by and large when there's been a problem, people have been willing to raise it, and the college has been willing to respond."

In a phone call yesterday, a Boston College representative tried to assure Vasquez, Allston-Brighton's community task force cochairman, that even though the church plans to sell its land to the college, the neighborhood would be far better off than if the land were to be sold for condominiums. But Vasquez was not convinced.

"Poppycock," he said. "We often hear this same argument from other institutions in our midst. If they have more land, then they're able to increase their enrollment and bring in more students. It's a cyclical issue that continues to destabilize the neighborhood."

David Abel and Mac Daniel of the Globe staff contributed to this report. Donovan Slack can be reached at dslack@globe.com.